TRPV4 is a member of the Transient Receptor Potential (TRP) superfamily of cation channels and is activated by heat, demonstrating spontaneous activity at 528 temperatures (Guler et al., 2002. J Neurosci 22: 6408-6414). Consistent with its polymodal activation property TRPV4 is also activated by hypotonicity and physical cell stress/pressure (Strotmann et al., 2000. Nat Cell Biol 2: 695-702), through a mechanism involving phospholipase A2 activation, arachidonic acid and epoxyeicosatrienoic acid generation (Vriens et al., 2004. Proc Natl Acad Sci USA 101: 396-401), In addition, amongst other mechanisms proposed, tyrosine kinase activity may also regulate TRPV4 (Wegierski et al., 2009. J Biol Chem. 284: 2923-33).
Heart failure results in the decreased ability of the left ventricle to pump blood into the peripheral circulation as indicated by a reduced ejection fraction and/or left ventricular dialation. This increases the left ventricular end diastolic pressure resulting in enhanced pulmonary blood pressures. This places the septal barrier, which separates the circulatory aqueous environment and the alveolar airspaces of the lung, at risk. Increased pulmonary pressure results in the flow of fluid from the pulmonary circulation into the alveolar space resulting in lung edema/congestion, as is observed in patients with congestive heart failure.
TRPV4 is expressed in the lung (Delany et al., 2001. Physiol. Genomics 4: 165-174) and has been shown to mediate Ca2+ entry in isolated endothelial cells and in intact lungs (Jian et al., 2009 Am J Respir Cell Mol Biol 38: 386-92). Endothelial cells are responsible for forming the capillary vessels that mediate oxygen/carbon dioxide exchange and contribute to the septal barrier in the lung. Activation of TRPV4 channels results in contraction of endothelial cells in culture and cardiovascular collapse in vivo (Willette et al., 2008 J Pharmacol Exp Ther 325: 466-74), at least partially due to the enhanced filtration at the septal barrier evoking lung edema and hemorrage (Alvarez et al., 2006. Circ Res 99: 988-95). Indeed filtration at the septal barrier is increased in response to increased vascular and/or airway pressures and this response is dependent on the activity of TRPV4 channels (Jian et al., 2008 Am J Respir Cell Mol Biol 38: 386-92). Overall this suggests a clinical benefit of inhibiting TRPV4 function in the treatment of heart failure associated lung congestion.
Additional benefit is suggested in inhibiting TRPV4 function in pulmonary-based pathologies presenting with symptoms including lung edema/congestion, infection, inflammation, pulmonary remodeling and/or altered airway reactivity. A genetic link between TRPV4 and chronic obstructive pulmonary disorder (COPD) has recently been identified (Zhu et al., 2009. Hum Mol Genetics, 18: 2053-62) suggesting potential efficacy for TRPV4 modulation in treatment of COPD with or without coincident emphysema. Enhanced TRPV4 activity is also a key driver in ventilator-induced lung injury (Hamanaka et al., 2007. Am J Physiol 293: L923-32) and it is suggested that TRPV4 activation may underlie pathologies involved in acute respiratory distress syndrome (ARDS), pulmonary fibrosis and asthma (Liedtke & Simon, 2004. Am J Physiol 287: 269-71). A potential clinical benefit for TRPV4 blockers in the treatment of sinusitis, as well as allergic and non-allergic rhinitis is also supported (Bhargave et al., 2008. Am J Rhinol 22:7-12).
In addition, TRPV4 channels have recently been implicated in urinary bladder function (Thorneloe et al., 2008. J Pharmacol Exp Ther 326: 432-42) and are likely to provide therapeutic benefit for conditions of bladder overactivity, characterized by an increased urge to urinate and an enhancement of micturition frequency. These data suggest a clinically beneficial effect of inhibiting TRPV4, located on multiple cell types, on urinary bladder function that is likely to be effective in bladder disorders such as overactive bladder, interstitial cystitis and painful bladder syndrome.
Furthermore TRPV4 has in recent years been implicated in a number of other physiological/pathophysiological processes in which TRPV4 antagonists are likely to provide significant clinical benefit. These include various aspects of pain (Todaka et al., 2004. J Biol Chem 279: 35133-35138; Grant et al., 2007. J Physiol 578: 715-733; Alessandri-Haber et al., 2006. J Neurosci 26: 3864-3874), genetic motor neuron disorders (Auer-Grumbach et al., 2009. Nat Genet. PMID: 20037588; Deng et al., 2009. Nat Genet PMID: 20037587; Landouré et al., 2009. Nat Genet PMID: 20037586), cardiovascular disease (Earley et al., 2005. Circ Res 97: 1270-9; Yang et al., 2006. Am. J Physiol. 290:L1267-L1276), and bone related disorders; including osteoarthritis (Muramatsu et al., 2007. J. Biol. Chem. 282: 32158-67), genetic gain-of function mutations (Krakow et al., 2009. Am J Hum Genet 84: 307-15; Rock et al., 2008 Nat Genet 40: 999-1003) and osteoclast differentiation (Masuyama et al. 2008. Cell Metab 8: 257-65).